Conventional gas operated weapons have a primary mass that is driven by gas tapped from the weapon bore through a port. This primary mass which typically is a piston or is operated by the piston, provides the kinetic energy and mechanical means for unlocking the bolt and driving the combined primary mass and secondary mass (bolt) rearwardly. This combination provides the kinetic energy and mechanical means for performing the functioning cycle of the mechanism, whereby a spent cartridge is ejected, a fresh cartridge is chambered and the firing pin placed at ready for triggering the next firing.
Gas operating systems can be designed to be strong yet light weight and which employ the highest pressure cartridges, but the weight to which the gas operating system can be reduced has heretofore been limited by the relationship between the primary and secondary masses. The smallest weight of the secondary mass (bolt) is limited by its several functions, i.e., locking carrying the firing pin, extractor, ejector, etc. Once the seondary mass is determined, the primary mass, which typically is a piston or is operated by the piston, is largely dictated by the ratio which must be provided between the two masses.